Device and method of video decoding with first and second decoding code

ABSTRACT

A video image decoding device receives, as the code string to be decoded, a first code string to be decoded including information based on an encoded residual coefficient and header information or a second code string to be decoded including a residual image obtained in encoding the code string to be decoded and header information. The video image decoding device, when the code string to be decoded that is received by the receiver is the first code string to be decoded, adds the residual decoded image and the predictive image to each other to generate and output a reconstructed image and, when the code string to be decoded received by the receiver is the second code string to be decoded, adds a residual image included in the second code string to be decoded and the predictive image to each other to generate and output a reconstructed image.

BACKGROUND 1. Technical Field

The present disclosure relates to a video image decoding device and avideo image decoding method that each decode encoded code strings.

2. Related Art

In recent years, with development of multimedia applications, it hasbeen popularized that information of all kinds of media such as images,sounds, and texts are uniformly handled. Since a digitized image hashuge volumes of data, an image information compression technique isindispensable to accumulate and transmit the image. On the other hand,to mutually operate compressed image data, standardization ofcompression techniques is also important. For example, as standards ofmeasure of image compression techniques, H.261, H.263, and H.264 ofITU-T (telecommunication standardization sector in InternationalTelecommunication Union), MPEG-1, MPEG-3, MPEG-4, and MPEG-4AVC ofISO/IEC (International Organization for Standardization), and the likeare given. At present, a standardization action for a next-generationscreen encoding scheme obtained by the collaboration between ITU-T andISO/IEC and called HEVC has been advanced.

In such encoding of a video image, each picture to be encoded is dividedinto encoding unit blocks, and redundancies in time and spatialdirections are reduced in units of blocks to compress an amount ofinformation. In inter predictive encoding to reduce a time redundancy,detection of motion and formation of a predictive image are performed inunits of blocks with reference to a forward or a backward picture toobtain a differential image between the obtained predictive image and aninput image of a block to be encoded. In intra predictive encoding toreduce a spatial redundancy, a predictive image is generated from pixelinformation of peripheral encoded blocks to obtain a differential imagebetween the obtained predictive image and an input image of a block tobe encoded. In addition, orthogonal transformation such as discretecosine transformation and quantization are performed to the obtaineddifferential image, and a code string is generated by usingvariable-length-coding to compress an amount of information.

In decoding, the code string generated by the encoding process isanalyzed to obtain prediction information and residual coefficientinformation, inter predictive decoding and intra predictive decoding areperformed by using the prediction information to generate a predictiveimage, inverse quantization and inverse orthogonal transformation areperformed to the residual coefficient information to generate adifferential image, and the obtained predictive image and thedifferential image are added to each other to decompress a final outputimage.

In H.264 (ITU-T H.264: Advanced video coding for generic audiovisualservices (March 2010)), in order to restrict an upper limit of an amountof processing in each block, a maximum value of an amount of codesgenerated in each block is defined (more specifically, 3200 bits). Whenthe above normal encoding process is performed, a code string includingan amount of code larger than the maximum value of the amount ofgenerated codes may be generated depending on the quality of an inputimage or conditions of a quantization process. For this reason, aspecial encoding mode called an IPCM is used to make it possible tosuppress the amount of code of the code string to be smaller than themaximum value.

The IPCM is different from a normal encoding mode, and is a mode inwhich pixel values of an input image are directly described as a bitstring in a code string without performing generation, orthogonaltransformation/quantization of a differential image by intra/interprediction. In use of the mode, for example, when the format of an inputimage is YUV4:2:0 in which each pixel has 8 bits, a block of a luminancecomponent has 16×16 pixels, and each block of two color-differencecomponents has 8×8 pixels. For this reason, the total number of bites is384 bytes, and the number of bits of the input image includinginformation required for a header can be suppressed in an amount equalto or smaller than 3200 bits, i.e., the maximum value described above.

SUMMARY

In a large number of video image encoding/decoding devices, anencoding/decoding process is achieved by an integrated circuit called anLSI. Such an encoding/decoding device employs a configuration thatenables a parallel operation called a pipeline to be performed toincrease a processing speed. More specifically, before a process of oneblock is completed, a process of the next block is started to cause theprocesses to simultaneously proceed.

FIG. 14(a) shows an example of a pipeline in encoding. To a block 1,processes including pixel loading, mode determination (determinationwhether a mode is set to an inter prediction mode or an intra predictionmode), inter/intra prediction, transformation/quantization, andvariable-length-coding are sequentially applied, and the same processesas described above are also applied to a block 2. At this time, theblock 2 starts the process immediately after pixel loading of the block1 is completed to perform processes in parallel to each other whileprocess timings are delayed every step. In the encoding/decoding processof H.264 or HEVC, since processes are executed with reference toinformation of blocks that encoded/decoded in the past, processes to theblock 2 is need to be executed with reference to process predictionintonation, pixel information, encoding information, and the like thatare fixed in the block 1 as shown in the drawing.

However, it cannot be determined whether the amount of code generated ineach block is suppressed in an amount equal to or smaller than themaximum value by an amount of code is examined upon completion of thevariable-length-coding. For this reason, if it is determined that theamount of code exceeds the maximum value, at this time, the mode must beswitched to the IPCM to generate a code string again.

FIG. 14(b) shows an example of a pipeline obtained when switching to theIPCM occurs. It is assumed that switching to the IPCM is fixed in thevariable-length-coding process in a block 1. However, at this time, in ablock 2, the encoding process has proceeded with reference to predictioninformation, pixel information, and the like obtained when the block 1performs normal encoding. For this reason, retuning to modedetermination in the block 1, the block 1 must update information thatis referred on the assumption that encoding is performed in the IPCM toperform the process in the block 2 again.

Controlling to retrace the pipeline requires very complex processingcontrol. When the number of times of retracing is increased when theIPCM occurs in a target picture many times, a decrease in processingspeed is caused, and an encoding process of the target picture cannot becompleted in the required time.

One non-limiting and exemplary embodiment provides a video imagedecoding device and a video image decoding method in which, when a videoimage encoding device has a pipeline structureconstructed to suppress anamount of code generated in units of blocks to be equal to or smallerthan a specific maximum value, can decode a code string encoded by thevideo image encoding device.

A video image decoding device according to a first aspect of thedisclosure is a video image decoding device that decodes a code stringto be decoded in units of blocks. The video image decoding deviceincludes a receiver that receives, as the code string to be decoded, (1)a first code string to be decoded including information based on anencoded residual coefficient and header information associated with theinformation or (2) a second code string to be decoded including aresidual image obtained in an encoding process step of the code stringto be decoded and header information associated with the residual image,a header analyzer that acquires at least prediction information servingas information related to a predictive image used in generating the codestring to be decoded from the header information, a coefficient codestring analyzer that variable-length-decodes the code string to bedecoded received by the receiver to output a residual coefficient, apredictive residual decoder that performs inverse quantization andinverse orthogonal transformation to a residual coefficient output fromthe coefficient code string analyzer to generate a residual decodedimage, a predictive encoder that generates a predictive imagecorresponding to the code string to be decoded based on the predictioninformation acquired by the header analyzer; and an adder that, when thecode string to be decoded that is received by the receiver is the firstcode string to be decoded, adds the residual decoded image generated bythe predictive residual decoder and the predictive image generated bythe predictive encoder to each other to generate and output areconstructed image and, when the code string to be decoded received bythe receiver is the second code string to be decoded, adds a residualimage included in the second code string to be decoded and thepredictive image generated by the predictive encoder to each other togenerate and output a reconstructed image.

A video image decoding device according to a second aspect of thedisclosure is a video image decoding device that decodes a code stringto be decoded in units of blocks. The video image decoding deviceincludes a receiver that receives, as the code string to be decoded, (1)a first code string to be decoded including information based on anencoded residual coefficient and header information associated with theinformation or (2) a second code string to be decoded including aresidual decoded image obtained by locally decoding a residualcoefficient obtained in an encoding process step of the code string tobe decoded and header information associated with the residual decodedimage, a header analyzer that acquires at least prediction intonationserving as intonation related to a predictive image used in generatingthe code string to be decoded from the header information, a coefficientcode string analyzer that variable-length-decodes the code string to bedecoded that is received by the receiver to output a residualcoefficient, a predictive residual decoder that performs inversequantization and inverse orthogonal transformation to a residualcoefficient output from the coefficient code string analyzer to generatea residual decoded image, a predictive encoder that generates apredictive image corresponding to the code string to be decoded based onthe prediction intonation acquired by the header analyzer, and an adderthat, when the code string to be decoded received by the receiver is thefirst code string to be decoded, adds the residual decoded imagegenerated by the predictive residual decoder and the predictive imagegenerated by the predictive encoder to each other to generate and outputa reconstructed image and, when the code string to be decoded receivedby the receiver is the second code string to be decoded, adds a residualdecoded image included in the second code string to be decoded and thepredictive image generated by the predictive encoder to each other togenerate and output a reconstructed image.

A video image decoding device according to a second aspect of thedisclosure is a video image decoding device that decodes a code stringto be decoded in units of blocks. The video image decoding deviceincludes a receiver that receives, as the code string to be decoded, (1)a first code string to be decoded including information based on anencoded residual coefficient and header information associated with theinformation or (2) a second code string to be decoded including aresidual image obtained in an encoding process step of the code stringto be decoded and header information associated with the residual image,a header analyzer that acquires at least prediction intonation servingas intonation related to a predictive image used in generating the codestring to be decoded from the header information, a coefficient codestring analyzer that, when the first code string to be decoded isacquired, variable-length-decodes and outputs the residual coefficientand, on the other hand, when the second code string to be decoded isacquired, variable-length decodes and outputs the residual image, apredictive residual decoder that performs inverse quantization andinverse orthogonal transformation to a residual coefficient output fromthe coefficient code string analyzer to generate a residual decodedimage, a predictive encoder that generates a predictive imagecorresponding to the code string to be decoded based on the predictioninformation acquired by the header analyzer; and an adder that, when thecode string to be decoded that is received by the receiver is the firstcode string to be decoded, adds the residual decoded image generated bythe predictive residual decoder and the predictive image generated bythe predictive encoder to each other to generate and output areconstructed image and, when the code string to be decoded received bythe receiver is the second code string to be decoded, adds a residualimage output by the coefficient code string analyzer and the predictiveimage generated by the predictive encoder to each other to generate andoutput a reconstructed image.

The present disclosure can also generate means included in the videoimage encoding device and processes equivalent to the means as a programor an integrated circuit.

According to the video image decoding device of each aspect of thepresent disclosure, a decoding process suitable for a first code stringto be decoded and a second code string to be decoded that are encoded bya video image encoding device depending on whether a PCM mode is set ornot can be performed to the first code string to be decoded and thesecond code string to be decoded. For this reason, the video imageencoding device can be configured such that the amount of code generatedin units of blocks can be set to be a specific maximum value whileenabling encoding in the PCM to be performed and while suppressingretracing a pipeline.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a video imageencoding device according to a first embodiment.

FIG. 2 is a flow chart of a code string generating process according tothe first embodiment.

FIG. 3 is a conceptual diagram for explaining an example of the syntaxof a code string generated in the first embodiment.

FIG. 4 is a conceptual diagram for explaining another example of thesyntax of the code string generated in the first embodiment.

FIG. 5 is a conceptual diagram for explaining still another example ofthe syntax of the code string generated in the first embodiment.

FIGS. 6A and 6B are conceptual diagrams for explaining pipeline controlof a video image encoding device according to the first embodiment.

FIG. 7 is a block diagram showing a configuration of a video imageencoding device according to a second embodiment.

FIG. 8 is a flow chart of a code string generating process according tothe second embodiment.

FIGS. 9A and 9B are conceptual diagrams for explaining pipeline controlof the video image encoding device according to the second embodiment.

FIG. 10 is a block diagram showing a configuration of a video imageencoding device according to a third embodiment.

FIG. 11 is a flow chart of a code string generating process according tothe third embodiment.

FIG. 12 is a block diagram showing a configuration of a video imagedecoding device according to a fourth embodiment.

FIG. 13 is a flow chart of a code string analyzing process according tothe fourth embodiment.

FIGS. 14A and 14B are conceptual diagrams for explaining pipelinecontrol of a conventional video image encoding device.

DETAILED DESCRIPTION First Embodiment

A video image encoding device according to a first embodiment will bedescribed below with reference to the drawings.

1. Configuration of Video Image Encoding Device

FIG. 1 is a block diagram showing a configuration of a video imageencoding device 100 according to the embodiment. The video imageencoding device 100 divides a video image input in units of pictures andperforms an encoding process in units of blocks to generate a codestring.

The video image encoding device 100 includes a picture memory 101, apredictive residual encoder 102, a predictive residual decoder 103, alocal buffer 104, a predictive encoder 105, a quantization valuedeterminer 106, a header code string generator 107, and a coefficientcode string generator 108.

The picture memory 101 accumulates input image signals 151 input inunits of pictures in a display order an re-arranges pictures in anencoding order. When the picture memory 101 accepts a read instructionfrom a subtracter 109 or the predictive encoder 105, the picture memory101 outputs an input image signal related to the correspondinginstruction. At this time, each picture is divided into encoding unitscalled a coding unit (to be referred to as a CU hereinafter) and eachconfigured by a plurality of pixels. The CU is, for example, a blockhaving 64 (horizontal)×64 (vertical) pixels, a block having 32(horizontal)×32 (vertical) pixels, a block having 16 (horizontal)×16(vertical) pixels, or the like. In the video image encoding device 100in the embodiment, the subsequent processes are performed in units ofCUs.

The predictive residual encoder 102 performs orthogonal-transformation adifferential image signal 152 output from the subtracter 109.Furthermore, the predictive residual encoder 102 performs quantizationof an orthogonal transformation coefficient of each obtained frequencycomponent to compress image information to generate a residual encodingsignal 153. The predictive residual encoder 102 outputs the generatedresidual encoding signal 153 to the predictive residual decoder 103 andthe coefficient code string generator 108. At this time, the predictiveresidual encoder 102 performs quantization of the orthogonaltransformation coefficient by using a quantization value signal 158determined in the quantization value determiner 106.

The predictive residual decoder 103 performs inverse quantization andinverse orthogonal transformation of the residual encoding signal 153output from the predictive residual encoder 102 to generate a residualdecoding signal 154. The generated residual decoding signal 154 isoutput to an adder 110.

The local buffer 104 stores a reconstructed image signal 155 output fromthe adder 110. The reconstructed image signal 155 is used in a predictedencoding process in encoding of pictures subsequent to the picture to beencoded at present. More specifically, the reconstructed image signal155 is referred to as pixel data when the pictures subsequent to thepicture to be encoded at present are encoded. The local buffer 104outputs the stored reconstructed image signal 155 as pixel data to thepredictive encoder 105 in response to a read instruction from thepredictive encoder 105.

The predictive encoder 105 generates a predicted image signal 156 byusing intra prediction or inter prediction based on an input imagesignal output from the picture memory 101. The predictive encoder 105outputs the generated predicted image signal 156 to the subtracter 109and the adder 110. When the inter prediction is used, the predictiveencoder 105 uses the reconstructed image signal 155 of a past picturethat has been encoded and accumulated in the local buffer 104. When theintra prediction is used, the predictive encoder 105 uses thereconstructed image signal 155 of a current picture of a CU that isadjacent to a CU to be encoded and has been encoded. A mode determiningmethod to select one prediction from intra prediction and interprediction is pertained by predicting a method that can makes an amountof information of a residual signal smaller than that in the otherprediction method.

The quantization value determiner 106, based on pictures stored in thepicture memory 101, sets a quantization value to be used when thedifferential image signal 152 is quantized in the predictive residualencoder 102. The quantization value determiner 106 outputs the setquantization value to the predictive residual encoder 102 and the headercode string generator 107. As a setting method of a quantization valuein the quantization value determiner 106, a quantization value settingmethod based on so-called rate control in which a quantization value isset to cause a bit rate of a code string signal 159 to be close to atarget bit rate may be used.

The header code string generator 107 performs variable-length-coding toa prediction information signal 157 output from the predictive encoder105, the quantization value signal 158 output from the quantizationvalue determiner 106, and control information related to other encodingcontrol to generate a code string. The prediction information includedin the prediction information signal 157 includes, for example,information representing an intra prediction mode, informationrepresenting an inter prediction mode, information representing a motionvector, information representing a reference picture, and the like. Thecontrol intonation is intonation that can be acquired before the processin the coefficient code string generator 108 and informationrepresenting an encoding condition applied in encoding of a CU. Forexample, the information includes a block encoding type, a blockdivision information, and the like.

The coefficient code string generator 108 additionally describes a codestring generated by variable-length-coding the residual encoding signal153 output from the predictive residual encoder 102 or a code stringobtained without variable-length-coding the residual decoding signal 154output from the predictive residual decoder 103 subsequently to a codestring generated by the header code string generator 107 to generate thefinal code string signal 159. The variable-length-coding mentioned hereincludes arithmetic encoding. The following is the same as the above.

More specifically, the coefficient code string generator 108 executesone mode of two modes are switched depending on an input signal. Thefirst mode is a mode in which the code string signal 159 is generatedfrom a code string obtained by variable-length-coding the residualencoding signal 153 output from the predictive residual encoder 102 anda code string output from the header code string generator 107 andoutput. The second mode is a mode in which the code string signal 159 isgenerated from the residual decoding signal 154 output from thepredictive residual decoder 103 and a code string output from the headercode string generator 107 and output. When the code string signal 159 isoutput by using the second mode, the residual decoding signal 154directly handles the residual decoding signal 154 as a code stringwithout variable-length-coding the residual decoding signal 154.

The subtracter 109 generates the differential image signal 152 servingas a difference value between an image signal read from the picturememory 101 and the predicted image signal 156 output from the predictiveencoder 105 and outputs the differential image signal 152 to thepredictive residual encoder 102.

The adder 110 adds the residual decoding signal 154 output from thepredictive residual decoder 103 and the predicted image signal 156output from the predictive encoder 105 to each other to generate thereconstructed image signal 155 and outputs the reconstructed imagesignal 155 to the local buffer 104 and the predictive encoder 105.

2. Method of Generating Code String Signal

A method of generating a code string signal in the header code stringgenerator 107 and the coefficient code string generator 108 will beconcretely described with reference to the flow chart in FIG. 2 .

The header code string generator 107 variable-length-codes theprediction information signal 157 generated, the quantization valuesignal 158, and other encoding control intonation as a result of theencoding process to generate a code string of header information (S401).

The coefficient code string generator 108 determines, by using the inputresidual encoding signal 153, whether there is a possibility that anamount of code generated by a CU to be encoded exceeds larger than apredetermined value (S402).

When it is determined that there is no possibility of excess in stepS402, an identifier representing that a coefficient is encoded in aResidual mode is encoded (S403). Subsequently, the residual encodingsignal 153 input as in conventional encoding is variable-length-coded(Residual mode) to generate a code string (S404).

On the other hand, when it is determined that there is a possibility ofexcess in step S402, an identifier representing that a coefficient isencoded in a PCM mode is encoded (S405). Subsequently, the inputresidual decoding signal 154 is directly added to the code stringwithout variable-length-coding the residual decoding signal 154 (S406)to generate a code string (PCM mode).

It is determined by using the input residual encoding signal 153 in stepS402 whether there is a possibility that the amount of code generated bythe CU to be encoded exceeds the predetermined value. However, it may bedetermined by using another method whether there is a possibility thatthe amount of generated code exceeds the predetermined value. Forexample, there is a method of determining, by using the code stringsignal 159, whether the amount of code exceeds the predetermined value.In this case, since a code string has been output from coefficient codestring generator 108 when the determination is made, in the code string,the process is performed such that the code string obtained byvariable-length-coding the residual encoding signal 153 is directlyreplaced with the input residual decoding signal 154.

In place of determination made in units of CUs, determination may bemade in units of sets each configured by a plurality of CUs or in unitsof other blocks.

3. Syntax

FIG. 3 is a diagram showing an example of a syntax :coding_unit( ) inunits of CUs in a code string generated by the embodiment.

At the head of the syntax, a code string obtained byvariable-length-coding information such as a predictive mode :pred_mode,prediction information :prediction_unit( ) and a quantization value:qp_value, each of which is generated by the header code stringgenerator 107, is described.

An identifier pcm_flag that is the identifier described in FIG. 2 isdescribed. When the identifier is 0, it means that a coefficient codestring is described in Residual_data( ) in a Residual mode. When theidentifier is 1, it means that a coefficient code string is described inpcm_data( ) in a PCM mode. A coefficient code string described inpcm_data( ) is, as described above, the residual decoding signal 154that is not variable-length-coded.

FIG. 4 is a diagram showing another example of a syntax :coding_unit( )in units of CUs in a code string generated by the embodiment. The syntaxis different from the syntax described in FIG. 3 in only thatcbp_yuv_root is used as an identifier in place of pcm_flag.

The identifier is used to show whether there are residual encodingsignals for each of luminance components and each of color-differencecomponents in conventional encoding. When the identifier ranges from 0to 7, it means that, as in a conventional technique, a coefficient codestring is described in Residual_data( ) in a Residual mode. When theidentifier is 8, it means that a coefficient code string is described inpcm_data( ) in the PCM mode. More specifically, 8th intonation is addedto the pieces of conventional intonation 0 to 7.

In this manner, a new function can be added without increasing an amountof code caused by adding a new identifier.

FIG. 5 is a diagram showing still another example of a syntax:coding_unit( ) in units of CUs in a code string generated by theembodiment. The syntax is different from the syntax described in FIG. 3in only that residual_data_flag is used as an identifier in place ofpcm_flag.

The identifier is used to show whether a target block includes aresidual encoding signal in other conventional encoding. Morespecifically, when the identifier is 0, it means that there is nocoefficient information as in a conventional technique. When theidentifier is 1, as in a conventional technique, coefficient informationrepresents that the coefficient code string is described inResidual_data( ) in the Residual mode. Furthermore, when the identifieris 2, it means that a coefficient code string is described in pcm_data() in the PCM mode.

For this reason, a signal that is present as an identifier in aconventional technique can be used in common to make it possible tosuppress an increase of an amount of code caused by adding a newidentifier.

The values of the syntaxes and the identifiers described in FIG. 3 ,FIG. 4 , and FIG. 5 are just examples to explain the embodiment. Thevalues of syntaxes and identifiers different from those of the contentsdescribed above may be allocated to realize the same functions asdescribed above.

The predetermined value in step S402 in FIG. 2 is an amount of codeobtained by adding a margin to an amount of code obtained by summing upan amount of code required when the residual decoding signal 154 isdirectly described as a code string and a maximum amount of coderequired when all pieces of information to be described in the headercode string are encoded. For example, when the format of an image isYUV4:2:0 in which each pixel has 8 bits and when the size of a CU to beencoded is 32×32 pixels, an amount of code required when the residualdecoding signal 154 is directly described as a code string is 1536bytes. In this case, the predetermined value may be an amount of codeobtained by summing the amount of code, a maximum amount of coderequired when all pieces of information to be described in the headercode string are encoded, and a margin. For example, a value of 13000bits is conceivable.

4. Pipeline Improving Effect

An example of a pipeline in the video image encoding device according tothe embodiment will be described with reference to FIGS. 6A and 6B.

FIG. 6A is a diagram showing control of a pipeline performed when acoefficient code string is generated in the Residual mode as a result ofdetermination in step S402 in FIG. 2 . Processes are performed accordingto the same flow of the conventional control described in FIG. 14A.

On the other hand, FIG. 6B is a diagram showing pipeline controlperformed when a coefficient code string is generated in the PCM mode asa result of determination in step S402 in FIG. 2 . In the embodiment, asdescribed above, in the first mode, the residual encoding signal 153generated by the predictive residual encoder 102 isvariable-length-coded to generate a coefficient code sting, and, in astate in which header information generated by the header code stringgenerator 107 is associated with the coefficient code string, thecoefficient code string and the header information are output. On theother hand, in the second mode, without variable-length-coding theresidual decoding signal 154 generated by the predictive residualdecoder 103, the residual decoding signal 154 is directly used as acoefficient code string, and, in a state in which header intonationgenerated by the header intonation code string generator 107 isassociated with the coefficient code string, the coefficient code stringand the header information are output. In this case, the residualdecoding signal 154 is based on the input image signal 151 that is thesame as the residual encoding signal 153. In the decoding device, whenthe residual encoding signal 153 is decoded by using predictioninformation configuring a combination to the signal, the same signal asthe residual decoding signal 154 can be obtained. More specifically,pixel information of a reconstructed image finally generated in thedecoding device in the first mode is the same as that in the secondmode. For this reason, even when the mode of a block 1 is switched tothe PCM mode, a change of prediction information described in the headercode string and re-encoding are not necessary. For this reason, aprocess in a block 2 in which an encoding process proceeds withreference to prediction infoimation and pixel infoimation of the block 1is not influenced at all. Thus, only a coefficient code string can bedirectly encoded in the PCM mode without retracing the pipeline.

When the residual decoding signal 154 is output, the signal does notneed to be decoded in the decoding device. For this reason, althoughprediction infoimation is not required to decode the signal, theprediction intonation is referred to in decoding or the like in theblock 2.

In this manner, in the video image encoding device according to theembodiment, encoding can be pertained by switching the mode to the PCMmode without retracing the pipeline, an amount of generated code inunits of blocks can be made equal to or smaller than a specific maximumvalue without decreasing a processing speed or increasing an amount ofprocessing.

5. Conclusion

The video image encoding device 100 according to the embodiment is thevideo image encoding device 100 that encodes an input video image inunits of blocks, and includes the predictive encoder 105 that generatesa predictive image corresponding to an image to be encoded, thesubtracter 109 that generates the differential image signal 152 betweenthe image to be encoded and the generated predictive image, thepredictive residual encoder 102 that performs an orthogonaltransformation process and a quantizing process to an output from thesubtracter 109 to generate the residual encoding signal 153, thepredictive residual decoder 103 that performs an inverse quantizingprocess and an inverse orthogonal transformation process to the residualencoding signal 153 to generate the residual decoding signal 154, theadder 110 that adds the predictive image generated by the predictiveencoder 105 and the residual decoding signal 154 generated by thepredictive residual decoder 103 to each other to generate thereconstructed image signal 155, the header code string generator 107that generates header information including at least predictioninformation used in generating the predictive image, and the coefficientcode string generator 108 that, in the first mode, variable-length-codesthe residual encoding signal 153 generated by the predictive residualencoder 102 to generate a coefficient code string, outputs thecoefficient code string and the header intonation in a state in whichthe header intonation generated by the header code string generator isassociated with the coefficient code string, in the second mode,directly uses the residual decoding signal 154 as a coefficient codestring without variable-length-coding the residual decoding signal 154generated by the predictive residual decoder 103, and outputs thecoefficient code string and the header infoimation in a state in whichthe header infoimation generated by the header code string generator isassociated with the coefficient code string.

More preferably, the coefficient code string generator 108 outputs thecoefficient code string, the header infoimation, and the identifier in astate in which an identifier representing whether inverse quantizationand inverse orthogonal transformation are pertained when the coefficientcode string is decoded is associated with the coefficient code stringand the header information.

More preferably, the identifier is an identifier that is shared by thecoefficient code string in the first mode and the coefficient codestring in the second mode, one of the pieces of identifier intonationrepresents that encoding is pertained as a coefficient code string inthe first mode, and the other represents that encoding is perfoimed as acoefficient code string in the second mode and represents whether theresidual encoding signal 153 is encoded or not.

Second Embodiment

A video image encoding device according to the second embodiment will bedescribed below with reference to the accompanying drawings.

1. Configuration of Video Image Encoding Device

FIG. 7 is a block diagram showing a video image encoding device 100-1according to the embodiment. The video image encoding device 100-1divides a video image input in units of pictures into blocks andperforms an encoding process in units of blocks to generate a codestring.

The video image encoding device 100-1 includes a coefficient code stringgenerator 108-1 in place of the coefficient code string generator 108 ofthe video image encoding device 100 in the first embodiment.

For descriptive convenience, the detailed description of the sameconfigurations as in the first embodiment will be omitted. Furtheimore,in FIG. 7 , the same numbers as in FIG. 1 denote blocks having the samefunctions as in FIG. 1 .

The coefficient code string generator 108-1 has a first mode in which acode string obtained by variable-length-coding the residual encodingsignal 153 output from the predictive residual encoder 102 isadditionally described subsequently to a code string generated by theheader code string generator 107 to generate a final code string signal159-1. Furtheimore, the coefficient code string generator 108-1 has asecond mode in which a code string obtained withoutvariable-length-coding the differential image signal 152 output from thesubtracter 109 is additionally described subsequently to a code stringgenerated by the header code string generator 107 to generate the finalcode string signal 159-1.

The second mode may be a mode in which a code string obtained byvariable-length-coding the differential image signal 152 output from thesubtracter 109 is additionally described subsequently to a code stringgenerated by the header code string generator 107 to generate the finalcode string signal 159-1.

The coefficient code string generator 108-1 executes the operationswhile switching the first mode and the second mode.

2. Method of Generating Code String

FIG. 8 is a flow chart showing a method of generating a code stringsignal in the header code string generator 107 and the coefficient codestring generator 108-1.

In this flow chart, the process in step S406-1 is performed in place ofthe process in step S406 in the flow chart in FIG. 2 in the firstembodiment.

More specifically, when it is determined in step S402 that an amount ofcode generated in a CU to be encoded may exceed a predetermined value,an identifier representing that a coefficient is encoded in the PCM modeis encoded (S405). Subsequently, the input differential image signal 152is directly added to the code string without being variable-length-coded(PCM mode) to generate a code string (S406-1). In the above description,the differential image signal 152 may be configured to bevariable-length-coded and output.

3. Syntax

A syntax in the embodiment and an identifier encoded in S405 are thesame as those in the first embodiment.

The predetermined value in step S402 in FIG. 8 is an amount of codeobtained by adding a margin to an amount of code obtained by summing upan amount of code required when a differential image (pixel value of thedifferential image signal 152) is directly described as a code stringand a maximum amount of code required when all pieces of information tobe described in the header code string are encoded. For example, whenthe format of an image is YUV4:2:0 in which each pixel has 8 bits andwhen the size of a CU to be encoded is 32×32 pixels, an amount of coderequired when the pixel value of the differential image signal 152 isdirectly described as a code string is 1536 bytes. An amount of codeobtained by summing up the amount of code described above and themaximum amount of code required when all pieces of information to bedescribed in the header code string are encoded is added with a margin,so that a value of 13000 bits or the like is conceivable as thepredetermined value.

4. Pipeline Improving Effect

An example of a pipeline in the video image encoding device according tothe embodiment will be described with reference to FIGS. 9A and 9B.

FIG. 9A is a diagram showing control of a pipeline performed when acoefficient code string is generated in the Residual mode as a result ofdetermination in step S402 in FIG. 8 . Processes are performed accordingto the same flow of the conventional control described in FIG. 14A.

On the other hand, FIG. 9B is a diagram showing control of a pipelineperformed when a coefficient code string is generated in the PCM mode asa result of determination in step S402 in FIG. 8 . In the embodiment, asdescribed above, in the first mode, a code string obtained byvariable-length-coding the residual encoding signal 153 output from thepredictive residual encoder 102 is additionally described subsequentlyto a code string generated by the header code string generator 107 togenerate the final code string signal 159-1. On the other hand, in thesecond mode, a code string obtained without variable-length-coding thedifferential image signal 152 output from the subtracter 109 isadditionally described subsequently to a code string generated by theheader code string generator 107 to generate the final code stringsignal 159-1. In this case, the residual encoding signal 153 is based onthe input image signal 151 that is the same as the differential imagesignal 152. For this reason, even though a block 1 is switched to thePCM mode, a change of prediction information described in the headercode string is unnecessary. However, in the decoding device, when theresidual encoding signal 153 is decoded by using prediction intonationconfiguring a combination to the signal, a signal different from thedifferential image signal 152 is generated. For this reason, pixelinformation of a reconstructed image signal finally obtained in thedecoding device when encoding is performed in the first mode isdifferent from that obtained when encoding is performed in the secondmode. At this time, an encoding process of block 2 that refers to pixelinformation of the block 1 proceeds. For this reason, even in a block 2,the process must be executed again such that the pixel information isreplaced. Thus, the process must retrace an inter/intra predictionprocess in the block 1. However, in comparison with the conventionalcontrol described in FIG. 14B, the number of processes to retracedecreases.

In this manner, the video image encoding device according to theembodiment can make an amount of processing to retrace the pipelinesmaller than that in a conventional technique. For this reason, anamount of code generated in units of blocks can be suppressed in anamount equal to or smaller than a specific maximum value whilesuppressing a decrease in processing speed or an increase in an amountof processing.

In the embodiment, a differential image obtained before an encodingprocess is encoded. For this reason, the quality of an image decided inthe corresponding video image decoding device can be improved.

5. Conclusion

The video image encoding device according to the embodiment is the videoimage encoding device 100-1 that encodes an input video image in unitsof blocks, and includes the predictive encoder 105 that generates apredictive image corresponding to an image to be encoded, the subtracter109 that generates the differential image signal 152 between the imageto be encoded and the generated predictive image, the predictiveresidual encoder 102 that performs an orthogonal transformation processand a quantizing process to an output from the subtracter 109 togenerate the residual encoding signal 153, the predictive residualdecoder 103 that performs an inverse quantizing process and an inverseorthogonal transformation process to the residual encoding signal 153 togenerate the residual decoding signal 154, the adder 110 that adds thepredictive image generated by the predictive encoder 105 and theresidual decoding signal 154 generated by the predictive residualdecoder 103 to each other to generate the reconstructed image signal155, the header code string generator 107 that generates headerinformation including at least prediction information used in generatingthe predictive image, and the coefficient code string generator 108-1that, in the first mode, variable-length-codes the residual encodingsignal 153 generated by the predictive residual encoder 102 to generatea coefficient code string, outputs the coefficient code string and theheader information in a state in which the header information generatedby the header code string generator is associated with the coefficientcode string, in the second mode, directly uses the differential imagesignal 152 as a coefficient code string without variable-length-codingthe differential image signal 152 generated by the subtracter 109, andoutputs the coefficient code string and the header information in astate in which the header intonation generated by the header code stringgenerator is associated with the coefficient code string.

The video image encoding device according to the embodiment is the videoimage encoding device 100-1 that encodes an input video image in unitsof blocks, and includes the predictive encoder 105 that generates apredictive image corresponding to an image to be encoded, the subtracter109 that generates the differential image signal 152 between the imageto be encoded and the generated predictive image, the predictiveresidual encoder 102 that performs an orthogonal transformation processand a quantizing process to an output from the subtracter 109 togenerate the residual encoding signal 153, the predictive residualdecoder 103 that performs an inverse quantizing process and an inverseorthogonal transformation process to the residual encoding signal 153 togenerate the residual decoding signal 154, the adder 110 that adds thepredictive image generated by the predictive encoder 105 and theresidual decoding signal 154 generated by the predictive residualdecoder 103 to each other to generate the reconstructed image signal155, the header code string generator 107 that generates headerintonation including at least prediction information used in generatingthe predictive image, and the coefficient code string generator 108-1that, in the first mode, variable-length-codes the residual encodingsignal 153 generated by the predictive residual encoder 102 to generatea coefficient code string, outputs the coefficient code string and theheader information in a state in which the header information generatedby the header code string generator is associated with the coefficientcode string, in the second mode, directly uses the differential imagesignal 152 as a coefficient code string while variable-length-coding thedifferential image signal 152 generated by the subtracter 109, andoutputs the coefficient code string and the header information in astate in which the header information generated by the header codestring generator is associated with the coefficient code string.

More preferably, the coefficient code string generator 108-1 outputs thecoefficient code string, the header information, and the identifier in astate in which an identifier representing whether inverse quantizationand inverse orthogonal transformation are pertained when the coefficientcode string is decoded is associated with the coefficient code stringand the header information.

More preferably, the identifier is an identifier that is shared by thecoefficient code string in the first mode and the coefficient codestring in the second mode, one of the pieces of identifier informationrepresents that encoding is performed as a coefficient code string inthe first mode, and the other represents that encoding is performed as acoefficient code string in the second mode and represents that there isthe encoded residual encoding signal 153 is encoded.

Third Embodiment

A video image encoding device according to a third embodiment will bedescribed below with reference to the accompanying drawings.

1. Configuration of Video Image Encoding Device

FIG. 10 is a block diagram showing a video image encoding device 100-2according to the embodiment. The video image encoding device 100-2divides a video image input in units of pictures and performs anencoding process in units of blocks to generate a code string.

The video image encoding device 100-2 includes a coefficient code stringgenerator 108-2 in place of the coefficient code string generator 108 ofthe video image encoding device 100 in the first embodiment.

For descriptive convenience, the detailed description of the sameconfigurations as in the first embodiment will be omitted. Furthermore,in FIG. 10 , the same numbers as in FIGS. 1 and 7 denote blocks havingthe same functions as in FIGS. 1 and 7 .

The coefficient code string generator 108-2 executes the operations suchthat two modes are switched depending on an input signal. A first modeis a mode in which a code string obtained by variable-length-coding theresidual encoding signal 153 output from the predictive residual encoder102 is additionally described subsequently to a code string generated bythe header code string generator 107 to generate a final code stringsignal 159-2. A second mode is a mode in which a code string obtainedwithout variable-length-coding a code string obtained by multiplyingeach coefficient of the residual decoding signal 154 by 1/N (N is anatural number) is additionally described subsequently to a code stringgenerated by the header code string generator 107 to generate the finalcode string signal 159-2.

2. Method of Generating Code String

FIG. 11 is a flow chart showing a method of generating a code stringsignal in the header code string generator 107 and the coefficient codestring generator 108-2.

This flow chart is different from the flow chart in FIG. 2 in the firstembodiment in only that the process in step S406-2 is performed in placeof the process in step S406 in the flow chart in FIG. 2 .

More specifically, when it is determined in step S402 that an amount ofcode generated in a CU to be encoded may exceed a predetermined value,an identifier representing that a coefficient is encoded in the PCM modeis encoded (S405). Subsequently, each coefficient of the input residualdecoding signal 154 is multiplied by 1/N and added to a code stringwithout being variable-length-coded (PCM mode) to generate a code string(S406-2).

3. Syntax

A syntax in the embodiment and an identifier encoded in S405 are thesame as those in the first embodiment.

4. Pipeline Improving Effect

An example of a pipeline in the video image encoding device according tothe embodiment is almost the same as those in FIGS. 9A and 9B, anddifferent points will be described below.

When the PCM mode is selected as a result of determination in step S402in FIG. 8 , a residual decoded image is multiplied by 1/N. However, theresidual decoded image must be multiplied by N in decoding to generate aresidual decoded image. For this reason, an error occurs in the range of±(N−1).

FIG. 9B is a diagram showing a pipeline control performed when acoefficient code string is generated in the PCM mode as a result ofdetermination in step S402 in FIG. 8 . When a block 1 is switched to thePCM mode, the prediction intonation described in the header code stringis not changed. However, the residual decoded image changes. For thisreason, an encoding process in a block 2 that refers to pixelinformation of the block 1 proceeds. As a result, the process must beperformed again after the pixel information is replaced. Thus, theprocess must retrace an inter/intra prediction process in the block 1.However, in comparison with the conventional control described in FIG.14B, the number of processes decreases.

In this manner, the video image encoding device according to theembodiment can make an amount of processing to retrace the pipelinesmaller than that in a conventional technique. For this reason, anamount of code generated in units of blocks can be suppressed in anamount equal to or smaller than a specific maximum value whilesuppressing a decrease in processing speed or an increase in an amountof processing.

In the embodiment, the residual decoded image is multiplied by 1/N. Forthis reason, the number of bits can be reduced.

When a value N is fixed, the value N does not need to be described onthe syntax. When the value N is to be described on the syntax, the valuemay be described ins fields to which one value for each picture isdescribed.

5. Conclusion

The coefficient code string generator 108-2 according to the embodiment,in the first mode, variable-length-codes the residual encoding signal153 to generate a first coefficient code string, and, in the secondmode, sets the differential decoded image multiplied by 1/N (N is anatural number) as a second coefficient code string.

The coefficient code string generator 108-2 according to the embodiment,in the first mode, variable-length-codes the residual encoding signal153 to generate the first coefficient code string, and, in the secondmode, sets the differential image signal 152 multiplied by 1/N (N is anatural number) as the second coefficient code string.

Fourth Embodiment

A video image decoding device according to a fourth embodiment will bedescribed below with reference to the accompanying drawings.

1. Configuration of Video Image Decoding Device

FIG. 12 is a block diagram showing a configuration of a video imagedecoding device 200 according to the fourth embodiment. The video imagedecoding device 200 performs a decoding process to a code stringgenerated by the video image encoding device described in the secondembodiment in units of blocks called coding units (CU) to generate anoutput image.

The video image decoding device 200 includes a header code stringanalyzer 201, a coefficient code string analyzer 202, a predictiveresidual decoder 203, a picture memory 204, a predictive decoder 205,and a quantization value determiner 206.

The header code string analyzer 201 performs variable length decoding toa header area of an input code string signal 251 in units of blocks toanalyze header information. The header code string analyzer 201 outputsa prediction information signal 256 obtained by analysis to thepredictive decoder 205. Furthermore, the header code string analyzer 201outputs quantization value intonation obtained by analysis to thequantization value determiner 206.

The coefficient code string analyzer 202 analyzes a coefficient codestring encoded subsequently to the header information analyzed by theheader code string analyzer 201. At this time, when the coefficient codestring is a residual encoding signal 252 as a result of analysis, thecoefficient code string analyzer 202 outputs the residual encodingsignal 252 to the predictive residual decoder 203. On the other hand,when the coefficient code string is a differential image signal 259 as aresult of analysis, the coefficient code string analyzer 202 outputs thedifferential image signal 259 to an adder 207 while bypassing thepredictive residual decoder 203. More specifically, when the coefficientcode string is the differential image signal 259, a generating processof a residual decoding signal 253 by the predictive residual decoder 203is not executed. When the coefficient code string isvariable-length-coded, the coefficient code string analyzervariable-length-decodes the coefficient code string and then outputs thedecoded coefficient code string as the residual encoding signal 252 orthe differential image signal 259. On the other hand, when thevariable-length-coding is not performed, the coefficient code stringanalyzer outputs the coefficient code string as the residual encodingsignal 252 or the differential image signal 259 withoutvariable-length-decoding the coefficient code string.

The predictive residual decoder 203 pertains inverse quantization andinverse orthogonal transfoimation the residual encoding signal 252 inputfrom the coefficient code string analyzer 202 to generate the residualdecoding signal 253. The predictive residual decoder 203 outputs thegenerated residual decoding signal 253 to the adder 207. At this time,the predictive residual decoder 203 controls inverse quantization byusing a quantization value signal 257 determined in the quantizationvalue determiner 206.

The predictive decoder 205 generates a predictive image signal 254 byusing intra prediction or inter prediction based on the predictioninformation signal 256 output from the header code string analyzer 201.The predictive decoder 205 outputs the generated predictive image signal254 to the adder 207. The predictive decoder 205, in use of the interprediction, uses a reconstructed image signal 255 of a past picture thatis accumulated in the picture memory 204 and has been decoded. Thepredictive decoder 205, in use of the intra prediction, uses thereconstructed image signal 255 of a current picture of a CU that isadjacent to a CU to be decoded and has been decoded. It is determinedaccording to the input prediction information signal 256 whether theintra prediction or the inter prediction is used.

The adder 207 adds the predictive image signal 254 output from thepredictive decoder 205 to the residual decoding signal 253 output fromthe predictive residual decoder 203 or the differential image signal 259output from the coefficient code string analyzer 202 to generate thereconstructed image signal 255. The generated reconstructed image signal255 is stored in the picture memory 204 and is finally output to thedisplay device as an output image signal 258 in units of pictures.

2. Method of Analyzing Code String

A method of analyzing a code string in the header code string analyzer201 and the coefficient code string analyzer 202 will be concretelydescribed with reference to the flow chart in FIG. 13 .

The header code string analyzer 201 performs variable length decoding toa header area of an input code string to analyze header information tooutput the generated prediction information signal 256, quantizationvalue information, and other decoding control information to the processblocks in FIG. 12 (S1201).

The coefficient code string analyzer 202 analyzes an identifier in stepS1202 and, in step S1203, determines whether the analyzed identifierrepresents that a coefficient is encoded in the PCM mode or acoefficient is encoded in the Residual mode.

In step S1203, when it is determined that the coefficient is encoded inthe Residual mode, variable length decoding is performed to acoefficient code string input by the same manner as that in aconventional technique to acquire the residual encoding signal 252 andoutputs the residual encoding signal 252 to the predictive residualdecoder 203 (S1204).

On the other hand, in step S1203, when it is determined that acoefficient is encoded in the PCM mode, the input coefficient codestring is directly replaced, as the differential image signal 259, withthe residual decoding signal 253 output from the predictive residualdecoder 203 without being variable-length-decoded to perform thesubsequent processes (S1205).

The processing method for a code string generated in the video imageencoding device 100-1 described in the second embodiment is describedhere. However, by the same processing method, a code string generated bythe video image encoding device 100 described in the first embodimentcan also be decoded. At this time, intonation acquired in step S1205 isreplaced with a residual decoding signal 252 obtained after the residualdecoding in the corresponding encoding device. However, the process canbe performed without discriminating the decoding processes from eachother.

A code string generated by the video image encoding device 100-2described in the third embodiment can be decoded by the same processingmethod described above without changing processes except for the processin which a signal obtained by multiplying coefficients of the residualdecoding signal 252 by N in the coefficient code string analyzer 202 instep S1205 is output as the residual decoding signal 252.

3. Syntax

A syntax of a code string subjected to a decoding process in theembodiment and an identifier analyzed in S1202 are the same as those inthe first embodiment.

4. Pipeline Improving Effect

By using the video image decoding device according to the embodiment,the video image encoding device that generates a code stringcorresponding to the video image decoding device can employ theconfiguration described in the first embodiment, and encoding can beperformed such that the mode is switched to the PCM mode withoutretracing the pipeline as in FIG. 6B. For this reason, an amount of codegenerated in units of blocks can be suppressed in an amount equal to orsmaller than a specific maximum value without decreasing a processingspeed or increasing an amount of processing.

Similarly, by using the video image decoding device according to theembodiment, the video image encoding device that generates a code stringcorresponding to the video image decoding device can employ theconfiguration described in the second embodiment or the third embodimentto make it possible to make an amount of processing to retrace thepipeline smaller than that in a conventional technique as shown in FIG.9B. For this reason, an amount of code generated in units of blocks canbe suppressed in an amount equal to or smaller than a specific maximumvalue while suppressing a decrease in processing speed or an increase inan amount of processing, and the quality of the decoded image can beimproved.

5. Conclusion

The video image decoding device 200 according to the embodiment is thevideo image decoding device 200 that decodes a code string to be decodedin units of blocks, includes the header code string analyzer 201 thataccepts a first code string to be decoded including information based onan encoded residual coefficient and header information associated withthe information or a second code string to be decoded including aresidual image obtained in an encoding process step of the code stringto be decoded and header information associated with the residual imageas the code string to be decoded, the header code string analyzer 201that acquires at least the prediction intonation serving as intonationrelated to a predictive image used in generating the code string to bedecoded from the header information, the coefficient code stringanalyzer 202 that variable-length-decodes the code string to be decodedaccepted by the header code string analyzer 201 to output a residualcoefficient, the predictive residual decoder 203 that performs inversequantization and inverse orthogonal transformation to the residualcoefficient output from the coefficient code string analyzer 202 togenerate a residual decoded image, the predictive decoder 205 thatgenerates a predictive image corresponding to the code string to bedecoded based on the prediction information acquired by the header codestring analyzer 201, and the adder 207 that, when the code string to bedecoded accepted by the header code string analyzer 201 is the firstcode string to be decoded, adds the residual decoded image generated bythe predictive residual decoder 203 and the predictive image generatedby the predictive decoder 205 to each other to generate and output areconstructed image and, when the code string to be decoded accepted bythe header code string analyzer 201 is the second code string to bedecoded, adds a residual image included in the second code string to bedecoded and the predictive image generated by the predictive decoder 205to each other to generate and output a reconstructed image.

The video image decoding device 200 according to the embodiment is thevideo image decoding device 200 that decodes a code string to be decodedin units of blocks, and includes the header code string analyzer 201that accepts a first code string to be decoded including information andheader information associated with the information based on an encodedresidual coefficient or a second code string to be decoded including aresidual decoded image obtained by locally decoding a residualcoefficient obtained in an encoding process step of the code string tobe decoded and header information associated with the residual decodedimage as the code string to be decoded, the header code string analyzer201 that acquires at least the prediction information serving asinformation related to a predictive image used in generating the codestring to be decoded from the header information, the coefficient codestring analyzer 202 that variable-length-decodes the code string to bedecoded accepted by the header code string analyzer 201 to output aresidual coefficient, the predictive residual decoder 203 that performsinverse quantization and inverse orthogonal transformation to theresidual coefficient output from the coefficient code string analyzer202 to generate a residual decoded image, the predictive decoder 205that generates a predictive image corresponding to the code string to bedecoded based on the prediction information acquired by the header codestring analyzer 201, and the adder 207 that, when the code string to bedecoded accepted by the header code string analyzer 201 is the firstcode string to be decoded, adds the residual decoded image generated bythe predictive residual decoder 203 and the predictive image generatedby the predictive decoder 205 to each other to generate and output areconstructed image and, when the code string to be decoded accepted bythe header code string analyzer 201 is the second code string to bedecoded, adds a residual decoded image included in the second codestring to be decoded and the predictive image generated by thepredictive decoder 205 to each other to generate and output areconstructed image.

The code string to be decoded preferably includes an identifierrepresenting whether a residual image obtained in the encoding processstep of the code string to be decoded is included in the code string tobe decoded, the adder 207, when the identifier represents that the codestring to be decoded does not include the residual image obtained in theencoding process step of the code string to be decoded, adds theresidual decoded image generated by the predictive residual decoder 203and the predictive image generated by the predictive decoder 205 to eachother to generate and output a reconstructed image and, when theidentifier represents that the code string to be decoded includes aresidual image obtained in the encoding process step of the code stringto be decoded, adds the residual image included in the second codestring to be decoded and the predictive image generated by thepredictive decoder 205 to each other to generate and output areconstructed image.

The code string to be decoded preferably includes an identifierrepresenting whether a residual decoded image obtained by locallydecoding a residual coefficient in the encoding process step of the codestring to be decoded is included in the code string to be decoded, theadder 207, when the identifier represents that the code string to bedecoded does not include the residual decoded image obtained by locallydecoding the residual coefficient obtained in the encoding process stepof the code string to be decoded, adds the residual decoded imagegenerated by the predictive residual decoder 203 and the predictiveimage generated by the predictive decoder 205 to each other to generateand output a reconstructed image and, when the identifier representsthat the code string to be decoded includes the residual decoded imageobtained by locally decoding the residual coefficient obtained in theencoding process step of the code string to be decoded, adds theresidual decoded image included in the second code string to be decodedand the predictive image generated by the predictive decoder 205 to eachother to generate and output a reconstructed image.

Preferably, when the header code string analyzer 201 accepts the secondcode string to be decoded, the predictive residual decoder 203 does notperform inverse quantization and the inverse orthogonal transformationto the coefficient code string.

Another Embodiment

A program including functions equivalent to the means included in thevideo image encoding device and the video image decoding devicedescribed in each of the embodiments is recoded on a recording mediumsuch as a flexible disk, so that the processes described in theembodiments can be easily executed in an independent computer system.The recording medium is not limited to a flexible disk, and a recordingmedium such as an optical disk, an IC card, or a ROM cassette on which aprogram can be recorded can be used.

Functions equivalent to the means included in the video image encodingdevice and the video image decoding device described in the embodimentsmay be generated as LSIs serving as integrated circuits. The integratedcircuits may be configured as one chip such that the chip includes someor all of the integrated circuits. Depending on degrees of integration,the LSI may be called an IC, a system LSI, a super LSI, or an ultra LSI.

The method of integrating circuits is not limited to that of an LSI, andthe integrated circuits may be realized by dedicated circuits or generalprocessors. After LSIs are manufactured, a programmable FPGA (FieldProgrammable Gate Array) or a configurable processor in which theconnections and settings of circuit cells in the LSIs can bereconstructed may be used.

Furthermore, when a technique of an integrated circuit that can bereplaced with the technique of an LSI appears because of the developmentof a semiconductor technique or other techniques derived from thesemiconductor technique, functional blocks may be integrated by usingthe techniques as a matter of course.

The present disclosure may be applied to a broadcasting wave recordingdevice such as a DVD recorder or a BD recorder that includes the videoimage encoding device and the video image decoding device describedabove and compresses and records a broadcasting wave transmitted from abroadcast station.

At least some of the functions of the video image encoding devices, thevideo image decoding device, and the modification thereof may becombined to each other.

INDUSTRIAL APPLICABILITY

The present disclosure is useful as a video image encoding device thatencodes pictures configuring an input image in, for example, a videocamera, a digital camera, a video recorder, a mobile phone, a personalcomputer, or the like to output the pictures as video image encodingdata or a video image decoding device that decodes the video imageencoding data to generate a decoded image.

What is claimed is:
 1. An image decoding method that decodes an image inan inputted code stream, on a coding unit-by-coding unit basis, whereineach coding unit is within a picture and has a data size smaller than adata size of the picture, and wherein the inputted code stream comprisessyntaxes of coding units, which are in the coding units, respectively, asyntax of a current coding unit includes mode information indicatingwhether a first mode or a second mode is applied for the current codingunit, and the syntax of the coding units is outside of a syntax of theprediction unit, said method comprising: performing coefficient codestring analyzing that, (1) when the inputted code stream is a first codestring including information based on an encoded residual coefficient,variable-length-decodes the first code string to output a residualcoefficient, and (2) when the inputted code stream is a second codestring including a variable-length-encoded differential image,variable-length-decodes the second code string to output thedifferential image; performing predictive residual decoding that, whenthe coefficient code string analyzer outputs the residual coefficient,performs an inverse quantizing process and an inverse orthogonaltransformation process on the outputted residual coefficient to output aresidual decoded image; performing predictive decoding that generates apredictive image, on a prediction unit-by-prediction unit basis, for thecurrent coding unit corresponding to the inputted code string based onprediction information, wherein the prediction unit is included in thecurrent coding unit; performing header code analyzing of the modeinformation included in the syntax of the current coding unit, which isin the current coding unit and outside of a syntax of the predictionunit, to determine whether the mode information included in the syntaxof the current coding unit indicates whether the first mode or thesecond mode has been applied to the current coding unit; and performingadding that, (1) when the syntax of the current coding unit indicatesthe first mode, adds the residual decoded image and the predictive imageto each other to generate and output a reconstructed image and, (2) whenthe syntax of the current coding unit indicates the second mode, addsthe differential image and the predictive image to each other togenerate and output a reconstructed image without the inversequantization process and the inverse orthogonal transformation processbeing performed.
 2. A non-transitory computer readable medium storing abitstream, the bitstream including: syntax information according towhich a computer performs a decoding process that decodes an image in aninputted the bitstream, on a coding unit-by-coding unit basis, whereineach coding unit is within a picture and has a data size smaller than adata size of the picture, and wherein the inputted the bitstreamcomprises syntaxes of coding units, which are in the coding units,respectively, a syntax of a current coding unit includes modeinformation indicating whether a first mode or a second mode is appliedfor the current coding unit, and the syntax of the coding units isoutside of a syntax of the prediction unit, said decoding processcomprising: performing coefficient code string analyzing that, (1) whenthe inputted code stream is a first code string including informationbased on an encoded residual coefficient, variable-length-decodes thefirst code string to output a residual coefficient, and (2) when theinputted code stream is a second code string including avariable-length-encoded differential image, variable-length-decodes thesecond code string to output the differential image; performingpredictive residual decoding that, when the coefficient code stringanalyzer outputs the residual coefficient, performs an inversequantizing process and an inverse orthogonal transformation process onthe outputted residual coefficient to output a residual decoded image;performing predictive decoding that generates a predictive image, on aprediction unit-by-prediction unit basis, for the current coding unitcorresponding to the inputted code string based on predictioninformation, wherein the prediction unit is included in the currentcoding unit; performing header code analyzing of the mode informationincluded in the syntax of the current coding unit, which is in thecurrent coding unit and outside of a syntax of the prediction unit, todetermine whether the mode information included in the syntax of thecurrent coding unit indicates whether the first mode or the second modehas been applied to the current coding unit; and performing adding that,(1) when the syntax of the current coding unit indicates the first mode,adds the residual decoded image and the predictive image to each otherto generate and output a reconstructed image and, (2) when the syntax ofthe current coding unit indicates the second mode, adds the differentialimage and the predictive image to each other to generate and output areconstructed image without the inverse quantization process and theinverse orthogonal transformation process being performed.